The present disclosure relates to an image forming apparatus such as a copier, a printer, a facsimile, and a multifunction peripheral having functions of those devices, and more specifically, the present disclosure relates to an image forming apparatus that uses a developer containing a toner and a magnetic carrier and develops an electrostatic latent image formed on a photosensitive member by allowing only the toner to be carried on a developing roller.
There are known a single-component developing method and a two-component developing method as methods adopted in developing devices to develop an electrostatic latent image formed on a photosensitive member functioning an image carrier. The two-component developing method, in which a developer containing a toner and a magnetic carrier is used, is capable of maintaining a stable charge amount of toner over a long period of time, and thus is suitable from the viewpoint of life extension. For example, a developing device adopting the two-component developing method holds therein a developer containing a toner and a magnetic carrier such that the developer is fed to a developing roller from an agitating member. The developing roller is provided with an internal magnet, and the magnet allows the developer to be carried on the surface of the developing roller as a magnetic brush. The developing roller rotates to convey the developer toward the photosensitive member. Furthermore, the developing device is provided with a regulation member that regulates the layer thickness of the developer on the developing roller in order to stabilize the amount of developer to be transferred toward the photosensitive member by the rotation of the developing roller. At a position where the outer circumferential surface of the developing roller and that of the photosensitive member face each other, only the toner contained in the developer carried on the developing roller is fed to the photosensitive member to visualize the electrostatic latent image carried on the photosensitive member into a toner image.
When the regulation member regulates the layer thickness of the developer to form a uniform layer of the developer on the surface of the developing roller, part of the toner contained in the developer is scraped off by the regulation member, and such part of the toner floats around the regulation member like a fume. The floating toner adheres to, and gradually collects on, a surface on the downstream side of the regulation member in the rotation direction of the developing roller. The accumulated toner comes off the regulation member to be conveyed by the developing roller to adhere to the photosensitive member, and the adhered toner is finally transferred to a recording medium to cause a defective image.
Thus, in image forming apparatuses, to remove accumulation of toner adhered to the regulation member, a developing bias power supply between the photosensitive member and the developing roller is turned off, the rotation of the photosensitive member is stopped, and further the developing roller is rotated in a direction that is reverse to the direction in which the developing roller is rotated during image formation.
Examples of the two-component developing method include many other methods in addition, to the above-described developing method. For example, there is a developing method where only the toner is carried on the developing roller in developing the electrostatic latent image formed on the photosensitive member. A developing device adopting this developing method includes a magnetic roller that is provided with an internal magnet which allows the magnetic roller to carry a developer containing a toner and a magnetic carrier on its surface as a magnetic brush, a developing roller that is disposed racing a photosensitive member and the magnetic roller, that carries on its surface the toner contained in the magnetic brush that is conveyed by the magnetic roller, and that feeds the carried toner to the photosensitive member, and a regulation member that is disposed a predetermined distance away from the magnetic roller, and that regulates the layer thickness of the developer on the surface of the magnetic roller.
With this developing device, when the toner is fed from the developing roller to the photosensitive member to develop an electrostatic latent image formed on the photosensitive member, residual toner remaining on the surface of the developing roller without being used to develop the electromagnetic latent image may come off from the surface of the developing roller to float around the developing roller. The floating toner falls onto the regulation member that is disposed to be opposed to the magnetic roller. The floating toner also adheres to such part of the internal wall of a developing container that faces the developing roller. Through repeatedly performed the image forming operations, the toner that falls down on the regulation member is accumulated, and more and more toner adheres to the internal wall of the development container, until it falls from the internal wail of the developing container as a cluster of toner. If the accumulated toner or the cluster of toner moves to the developing roller and falls into a gap between the magnetic roller and the regulation member, it will disadvantageously result in a defective image having a defect such as an unwanted vertical line.
The present disclosure aims to provide an image forming apparatus that allows toner alone to be carried on a developing roller to develop an electrostatic latent image formed on an image carrier, and that collects toner that floats around the developing roller without being fed to the image carrier.